Nilotonia (Dartonia) sketi, Pešić, Vladimir, 2013

Pešić, Vladimir, 2013, A remarkable new Nilotonia species (Acari, Hydrachnidia, Anisitsiellidae) from percolating water of a cave in Cat Ba island in Halong Bay, Vietnam, Zootaxa 3710 (4), pp. 372-380 : 373-377

Nilotonia (Dartonia) sketi sp. nov.

( Figs. 1–3 )

Material examined. Holotype male (SMF), dissected and slide mounted, Vietnam, W of Vinh Ha Long, Cat Ba National Park, Dao Cat Ba (= Cat Ba Island), Trung Trang Cave, pools of percolated water, 14.06.2003, Sket & Trontelj. Paratypes: one female, same data as holotype, dissected and slide mounted (SMF).

Diagnosis. Dorsum as typical for the subgenus; suture line Cx-III/IV complete; P-2 with short ventral seta (ratio seta L/ventral segment L 2.8–3.0); P-4 very slender (L/H ratio 3.7), distinctly longer than P-2; legs bearing many heavy setae; claws of I – III-L well developed with one ventral clawlet; IV-L-6 without claws, with two fine denticle-like setae (possibly remnant of a claw), ventrally with a line of longer setae, and two elongated and slender subterminal setae, extending far beyond tip of segment; no sexual dimorphism in the legs.

Description. General features—Integument soft, with a fine, dense lineation ( Fig. 1C ); dorsum with a pair of postocular platelets and the posterior plate, posterodorsal plate nearly round (L/W ratio 0.8). Ocular pigment absent. Coxal field: Cx-I separated medially; suture line Cx-I/II and Cx-III/IV complete; Cxgl-4 slightly approached to the anterior margin of Cx-III; anterior to genital field medial margins of Cx-III slightly pointed. Genital field ( Figs. 2A–B ) with three pairs of elongated acetabula flanking gonopore all over its length; pregenital sclerite small and triangular, postgenital sclerite larger; excretory pore without sclerotization. Gnathosoma ( Fig. 2D ) compact, rostrum short. Palp ( Fig. 2E–F ): P-2 with short ventral seta (ratio seta L/ventral segment L 2.8–3.0); P-4 very slender (L/H ratio 3.7), distinctly longer than P-2, ventral group of denticles and setae close to distal segment margin dividing segment in ratios 1: 2.1–2.5. Legs: for shape and chaetotaxy of leg segments, see Figs. 3A–E : claws of legs I – III well developed with one ventral clawlet; IV-L-5 with a line of ventral setae, distally with three heavy distal setae (central of them elongated); IV-L-6: Fig. 3D–E , the distalmost seta long and slender, 9–10 µm away from tip of segment.

Male—Idiosoma L/W 980/900; posterodorsal plate L/W 91/115; coxal field L/W 475/809, Cx-III W 494; genital field L/W 189/108, ratio 1.75. Ejaculatory complex L 184. Palp: total L 536, dL/H, dL/H ratio: P-1, 35/57, 0.61; P-2, 163/90, 1.8; P-3, 97/74, 1.3; P-4, 190/51, 3.7; P-5, 51/21, 2.4; L P-2/P-4 ratio, 0.86; P-2 ventral seta L 42, ratio seta L/ventral segment L 2.8; gnathosoma vL 198; chelicera total L 375, claw L 103, basal segment L 280, ratio basal segment L/claw L 2.7. Legs: L of I-L-1–6: 78, 86, 116, 150, 184, 203; L of II-L-1–6: 83, 108, 128, 191, 222, 208; L of III-L-1–6: 108, 120, 141, 238, 269, 223; L of IV-L-1–6: 163, 128, 169, 263, 266, 250–255; IV-L-6 subterminal seta 1, L 136, basal W 4–5, subterminal seta 2, L 128.

Female—Idiosoma L/W 1060/980; posterodorsal plate L/W 92/109; coxal field L/W 475/869, Cx-III W 497; genital field L/W 209/142, ratio 1.5; postgenital sclerite smaller than in male. Palp: total L 545, dL/H, dL/H ratio: P-1, 33/59, 0.57; P-2, 163/91, 1.8; P-3, 100/72, 1.39; P-4, 197/54, 3.7; P-5, 52/21, 2.5; L P-2/P-4 ratio, 0.83; P-2 ventral seta L 39–42, ratio seta L/ventral segment L 2.8–3.0; chelicera total L 378, claw L 100, basal segment L 278, ratio basal segment L/claw L 2.8. Legs: L of I-L-2–6: 103, 123, 155, 181, 175; L of II-L-2–6: 108, 131, 193, 224, 205; L of III-L-1–6: 109, 128, 150, 241, 272, 222; L of IV-L-1–6: 116, 134, 169, 247, 278, 263; IV-L-6 subterminal seta 1, L 135, basal W 4–5, subterminal seta 2, L 122.

Etymology. The species is named after Prof. Boris Sket (Ljubljana, Slovenia).

Remarks. The new species is assigned to the subgenus Dartonia K. Viets, 1929 (see below for a discussion on the species assigned to this subgenus). The combination of absence of lateral eyes, the complete suture between Cx-III and Cx-IV, the claws of legs I – III bearing one ventral clawlet and the IV-L-6 ventrally with a line of longer setae, and two elongated and slender subterminal setae, is unique and will easily separate the new species from all other species of the subgenus.

In the setation of IV-L-6 (with two long subterminal setae) the new species agrees with Nilotonia bisetosa Smit & Pešić, 2010 ( Oman) and Nilotonia navina Cook, 1967 ( India) , both assigned to the subgenus Dartiella by Panesar (2003), and to Nilotonia caerulea (K. Viets, 1929) (Sumatra) and N. nifymanana Goldschmidt, 2008 ( Madagascar) , two species assigned to the subgenus Dartonia in the abovementioned system. All these species differ from N. sketi sp. nov. in the presence of well developed lateral eyes. Furthermore, N. bisetosa differs in having a ventral comb of I-III-L claws, P-2 with a longer ventral seta (length> ventral segment length) and a convex ventral surface covered by fine denticulation, and a much shorter I-L-6 (Smit and Pešić 2010). Nilotonia caerulea (K. Viets, 1929) is unique in having medially fused Cx-I and the ventral seta of P-2 short and thickened rather than hair-like (see Viets 1935). Nilotonia nifymanana Goldschmidt, 2008 differs in more compact palps (especially the expanded P-2 with ventral denticles and long ventral seta), and leg claws with comb-like ventral clawlets (see Goldschmidt 2008). Nilotonia navina Cook, 1967 , known only from a single female specimen from India (Cook 1967) originally was assigned to Dartonia , but later on moved by Panesar (2003) to Dartiella . This species differs in the shape of subterminal setae of IV-L-6 (subterminal seta stouter, preceding seta shorter, not extending over tip of segment); P-2 with long ventral seta (length> ventral segment length), and convexly protruding ventral margin in the area anterior to ventral seta insertion; P-4 more robust, as long as P-2; distal segments of I-L much stockier (I-L-6 L/H ratio 2.6, calculated from Cook’s figure) (see Cook 1967).

Distribution. Known only from the type locality, in Trung Trang Cave, on Cat Ba Island in the Gulf of Tonkin, northeastern Vietnam.

Notes on habitat. The type locality is a large shallow pool of percolated water in a long tunnel cave located in National in Park on Cat Ba Island; the cave is managed for tourists, but little adapted (Sket, pers. communication). Cat Ba is largest island (140 km 2) in the Cat Ba Archipelago, in the world-famous Ha Long Bay; more than half of the main island is a National Park, which is home to the highly endangered Cat Ba langur— Trachypithecus poliocephalus poliocephalus (Trouessart) . Accompanying fauna at the type locality includes a moderately dense population of a tiny stygobiontic bathynellid ( Paraeobathynella vietnamensis Camacho ), cyclopoid copepods, ostracods, decapods of the genus Tiwaripotamon Bott and gastropods of the genus Systenostoma Bavay and Dautzenberg ; insects are represented by larvae of Culicidae and some other Diptera (information provided by Boris Sket).

Figures

FIGURE 1 A – E. Nilotonia sketi sp. nov., male: A = idiosoma, ventral view; B = idiosoma, dorsal view; C = detail of dorsal integument. D – E Photographs of coxal and genital field: D = male; E = female. Scale bars = 100 µm.

FIGURE 2 A – G. Nilotonia sketi sp. nov. (A, D, F—male; B – C, E, G—female): A – B = genital field; C = IV-L- 5 and 6; D = gnathosoma; E = palp (P- 1 missing); F = palp; G = chelicera. Scale bars = 100 µm.

FIGURE 3 A – E. Nilotonia sketi sp. nov., male: A = I-L- 2 – 6; B = II-L; C = III-L; D = IV-L; E = IV-L- 6. Scale bars = 100 µm.